1. Field of the Invention
The present invention relates to a method of inter-layer search in a disk drive, which drives a multi-layer disk having a plurality of recording layers, and, more particularly, to a method of inter-layer search adaptable to a multi-layer random access memory (RAM) disk.
2. Description of the Related Art
As is well known, optical disks, such as compact disks (CDs) and digital versatile disks (DVDs), which have larger storage capacity than CDs, are used as storage media.
These optical disks are largely classified into two types, these two types being read-only optical disks and writable optical disks. The former includes CDs for read only memory (CD-ROMs) and DVDs for read only memory (DVD-ROMs), and the latter is also divided into a write once read many (WORM) type, in which data can be written only once but can be read any number of times, and a random access memory (RAM) type. The WORM type includes recordable CDs (CD-Rs) and recordable DVDs (DVD-Rs), and the RAM type includes rewritable CDs (CD-RWs) and DVD-RAMs.
In the meantime, a multi-layer disk having a plurality of recording layers formed on one side thereof is used to increase storage capacity. While a DVD-RAM with a single-sided/single layer structure has a storage capacity of 4.7 Gbyte, a DVD-RAM with a single-sided/double layer structure has a storage capacity of 9.4 Gbyte.
FIG. 1 is a schematic diagram of a multi-layer disk. Referring to FIG. 1, a multi-layer disk comprises of a bottom layer 100 and a top layer 102. Information recorded in the respective layers 100 and 102 is reproduced using a laser beam emitted from a laser diode (not shown). To read accurately the information recorded in the bottom layer 100 and the top layer 102, the laser beam must be focused exactly on the respective layers 100 and 102. The focus of the laser beam is adjusted by moving an objective lens 110 vertically, that is, in an optical axial direction relative to the multi-layer disk.
When reproducing information from a multi-layer disk as shown in FIG. 1, since data is scattered to be recorded in layers, there must be an ability to reproduce information recorded in one of the layers and then reproduce information recorded in the other layer subsequently. In that case, a focal point of a laser beam is shifted from one layer to the other layer by moving the objective lens 110 in the optical axial direction. This procedure is referred to as a layer jump.
FIGS. 2A and 2B are diagrams illustrating the configuration of recorded data in the multi-layer disk shown in FIG. 1. In detail, FIG. 2A illustrates the recorded data in a multi-layer ROM disk and FIG. 2B illustrates the recorded data in a multi-layer RAM disk.
Referring to FIGS. 2A and 2B, a dotted area represents an area where user data is recorded, a hatched area represents an area where dummy data is recorded, and a blank area represents an area where neither user data nor dummy data is recorded.
In the case of the multi-layer ROM disk, as shown in FIG. 2A, dummy data is recorded in an area where user data is not recorded, as additional recording cannot be done. Meanwhile, in the case of multi-layer RAM disk, as shown in FIG. 2B, an area where user data is not recorded is left intact in preparation for additional recording, and therefore no dummy data is recorded in that area.
FIG. 3 is a flow chart illustrating a conventional method of inter-layer search in a multi-layer disk drive.
Referring to FIG. 3, in operation S302, a layer jump is first performed if it is necessary to search the other layer of the multi-layer disk. The layer jump is performed by applying a focus jump pulse to a focus actuator in order to move an objective lens toward a target layer and then focusing a laser beam on the target layer using a focus error signal.
Next, in operation S304, after the focus is adjusted on the target layer, a target address is searched for.
The conventional method of inter-layer search as shown in FIG. 3 is effective for multi-layer ROM disks. There is a problem, however, when the conventional method is applied to multi-layer RAM disks, because a search time could be too long due to the area where user data is not recorded.
More particularly, most disk drives read an address using identification (ID) information of a header, especially during a reproduction operation, in order to reduce an access time. However, a RAM disk may include an area where user data, which includes the header, is not recorded. In the case in which a pickup unit is positioned due to a layer jump into the area where user data is not recorded, it is impossible to read the address using ID information of a header.
Accordingly, the address is read using a wobble signal instead of ID information in the header. In this case, however, since it requires a certain amount of time in order to convert a spindle servo operation, control gains, set a rotational speed of a spindle motor, and so on, the access time will be increased as a whole.
As the access time increases, product competitiveness may decrease. Accordingly, there is a demand for a method of inter-layer search in a disk drive to drive a multi-layer RAM disk, which can reduce an access time.